Frictional dampers are currently used in bracket designs to provide a constant friction force between surfaces to allow damping and misalignment in tube systems. Basically, a frictional damper transforms the kinetic energy of the system into work in the bracket and then dissipates a portion of that work via heat due to friction.
Used in a static application, stresses due to the misalignment of the system will be reduced. For example, sliding of the mating frictional surfaces may be designed to occur to relieve thermal stresses between two components. When sufficient force is exerted on the bracket parallel to the mating surfaces, the static friction force due to a normal spring load will be overcome and sliding will occur. This misalignment capability will reduce thermal stresses in the system.
The foregoing concept is also valid when applied to dynamic systems in vibration. When the amplitude of vibratory displacement exceeds a certain amount, the frictional damper activates. However, in all applications for a frictional damper of conventional design, the opposing frictional force remains constant during the vibratory displacement. Therefore, as the input increases, the response of the system will also increase uncontrollably.
A frictional damper for damping vibratory displacement of a motor or engine is disclosed in U.S. Pat. No. 1,751,743 to Link. This frictional damper comprises an upwardly extending bar connected to the motor or engine. The end of that bar is seated between a pair of opposing flat friction faces which bear against respective sides of the upwardly extending bar. A pair of springs compress this sandwich construction to a degree such that the upwardly extending bar is able to slide between the friction faces upon overcoming the frictional forces opposing such sliding. These frictional forces, which remain constant, act to damp engine vibrations.
U.S. Pat. No. 3,362,504 to Maldarelli discloses a mechanical damper comprising a damper pad which is pushed against a damper plate in response to downward displacement of a lever block connected to a vibrating component. At the same time, the displaced lever block urges the damper pad to slide relative to the damper plate. A friction force is thus generated which resists motion parallel to the plane of the damper plate and has a magnitude equal to the product of the force of the damper pad against the damper plate and the coefficient of friction of the two surfaces. The friction force produced resists the motion of the damper pad and is transmitted via intermediate elements to the lever arm. Thus the kinetic energy of whatever is producing force (i.e., the device being damped) is converted to heat (friction between the damper pad and the damper plate) and its movement is consequently damped. The lever arm and the damper pad are coupled via a roller bearing which bears against a plane inclined relative to the direction of translation of the lever arm. The magnitude of the damping action can be adjusted by setting the angle of the inclined plane.
U.S. Pat. No. 3,690,413 to Airheart discloses a two-stage motion damper. In the first stage a frictional damper damps oscillations in response to the force exerted by yieldable means (e.g., Belleville washers). The frictional damper comprises a pair of displaceable members which slide with friction between respective pairs of opposing friction pad surfaces. In response to displacement of the displaceable member beyond a predetermined point, additional force is applied to the damper by a fluid pressure-responsive actuator.